Method for repairing an upstream rail of a turbine engine turbine casing

ABSTRACT

A method for repairing an upstream rail of a turbine engine turbine casing, the casing including a casing body extending along a longitudinal axis, the upstream rail including: a base including a radial surface, extending substantially radially from the casing body; a plate including an upper surface, extending substantially along the longitudinal axis; and a connection portion between the base and the plate, including a concave surface connecting the radial surface and the upper surface, the concave surface and the radial surface extending on either side of an edge, the method including: covering a surface with a solder, the surface including the upper surface and the concave surface, such that the solder extends substantially until the edge; and a step of machining the covered surface, in a single action, in the direction of the radial surface, and at least until the edge, so as to reshape the surface.

TECHNICAL FIELD OF THE INVENTION

The invention relates to the general field of members of turbineengines. It more particularly relates to a method for repairing anupstream rail of a turbine engine turbine casing.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

The aeronautical turbine engines conventionally comprise several modulessuch as a high pressure compressor, a combustion chamber, a highpressure turbine followed by a low pressure turbine, which drive thecorresponding LP or HP compressor, and a gas discharge system. Each ofthe turbines is formed with one or more stages, each stage successivelyincluding a stationary vane impeller or nozzle guides and a moving vaneimpeller.

Moving vanes are carried at their lower part by the turbine engine rotorand attached to a turbine disc. In contrast, nozzle guide vanes are heldby their upper part and attached to a casing, referred to as turbinecasing. The terms “lower” and “upper” are to be considered relatively toa distance to the turbine engine axis: the lower part of a piece, whensaid piece is fitted in the turbine engine, is closer to the turbineengine axis than the upper part of said piece.

With reference to FIG. 1, a turbine casing 10 has, in a longitudinalcross-section, a casing body 11 on which a plurality of rail couples 12is attached, each rail couple 12 being comprised of an upstream annularrail 13 and of a downstream annular rail 14, each rail couple 12 beingintended to hold guide nozzles 15 of a turbine stage. There are thus asmany rail couples as turbine stages. The terms “upstream” and“downstream” are to be considered relative to a general direction offlow of fluids through the turbine engine, from upstream to downstream.

The upstream rails 13 each include a plate 16 extending axially (withreference to the axis of rotation of the turbine engine) downstream. Oneach upper face of the plate 16 of the upstream rail 13, an upstreamhook 17 of a nozzle guide is placed, integral with a platform of thenozzle guide 18, which also extends axially upstream. The nozzle guide18 is carried at its downstream end by the downstream rail 14 associatedwith the considered upstream rail 13.

After a certain working time, a wear of the upper faces of the plates ofthe upstream rails is noticed, resulting from micro-displacementscreated by vibrations and a thermal expansion differences between theupstream rails and upstream hooks. This wear can alter the tilt ofnozzle guides which can then tip over around the downstream rails anddegrade the engine operation.

Thus, when an upper face of an upstream rail is damaged, it is necessaryto repair the rail.

A known repairing method consists in covering the upper face of the railwith a solder by welding, in order to add material, then in machiningthe covered face. However, this repairing method has a major drawback.The upper face is joined to a concave surface of a highly strained railportion. A machining springback, that is a geometric discontinuity dueto the exit of the machining tool, is therefore forbidden in the concavesurface. Indeed, a springback would lead to a significant stressembrittling a highly strained portion. Yet, given the welding accuracy,which is in the order of a few millimetres, the solder may sometimesoverflow up to the concave surface. It is thus impossible to suppressthis solder, since machining the concave surface would lead to aspringback in the concave surface.

Moreover, this repairing method does not enable the concave surface ofthe rail to be repaired when it is damaged.

GENERAL DESCRIPTION OF THE INVENTION

The object of the invention is to provide a repairing method enabling anupstream rail to be repaired while avoiding a machining springback inthe concave area, and further enabling said concave area to be repairedif it is damaged.

A first aspect of the invention therefore relates to a method forrepairing an upstream rail of a turbine engine turbine casing, saidupstream rail being intended to support an upstream hook of a nozzleguide of a stage of said turbine.

The upstream rail includes:

-   -   a base including a face, referred to as radial face, extending        substantially radially from the casing body    -   a plate including a face, referred to as upper face, extending        substantially along the longitudinal axis    -   a connection portion between the base and the plate, including a        concave face connecting the radial face and the upper face, the        concave face and the radial face extending on either side of an        edge.

The repairing method includes:

-   -   a step of covering a surface with a solder, said surface        including the upper face and the concave face, so that said        solder extends substantially until the edge    -   a step of machining the covered surface, in a single action, in        the direction of the radial face, and at least until the edge,        so as to reshape the surface.

Since machining is performed in a single action at least until the edgedelimiting the concave face, a springback in the concave face isavoided. Furthermore, wears of the concave face are suppressed without athickness loss of the connection portion.

Further to the characteristics which have just been mentioned in theprevious paragraph, the method according to the invention can have oneor more additional characteristics among the following, consideredindividually or according to any technically possible combinations.

In a non-limiting embodiment, machining the covered surface is performedso as to end in the radial face. The machining springback is thuslocalised on the radial face, which is the least strained area of theupstream rail.

In a non-limiting embodiment, the method includes a further step ofmachining the radial face. This step makes it possible to suppresssolder residues which could have disseminated on the radial face. It isnoted that the machining depth must be small so as not to embrittle thebase. The machining depth is for example in the order of 0.1 millimetre.

In a non-limiting embodiment, covering is performed by Tungsten InertGas (TIG) welding, which enables a simple accurate welding.

In a non-limiting embodiment, the covered surface includes a side faceand a lower face of the plate. Thus, machining in a single action startsat the lower face of the plate. The plate is then fully reshaped.

In a non-limiting embodiment, the solder is of the same material as theupstream rail. Thus, the rail reshaped by the method has no materialdiscontinuities.

A second aspect of the invention relates to an upstream rail of aturbine engine turbine casing, repaired through a method according tothe first aspect of the invention.

The invention and its numerous applications will be better understoodupon reading the following description and upon studying theaccompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

Figures are presented purely by way of indicating and in no way limitingexample of the invention. Figures show:

in FIG. 1, already described, a schematic representation of a casingincluding rails to support a nozzle guide

in FIG. 2, a schematic representation of an upstream rail of the casingof FIG. 1, in a cross-section view

in FIG. 3, a schematic representation of the steps of an embodiment ofthe method according to the first aspect of the invention

in FIG. 4, a schematic representation of the upstream rail of FIG. 2,depicting a covering step of the method

in FIG. 5, a schematic representation of the upstream rail of FIG. 3,depicting a machining step of the method.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

FIG. 2 shows a turbine engine casing 19, said turbine engine generallyextending along a longitudinal axis. More precisely, FIG. 2 is a partialview of the casing in a longitudinal cross-section view. Said casing 19includes a generally cylindrical casing body 21, and a plurality ofrails among which an annular upstream rail 20.

In a longitudinal cross-section, the upstream rail 20 has the generalshape of an L, and thus includes several parts:

-   -   a base 22 integral with the casing body 21, extending        substantially radially from the casing body 21 in the direction        of the longitudinal axis    -   a plate 23 extending substantially longitudinally from upstream        to downstream    -   a connection portion 24 connecting the base 22 and the plate 23.

By “substantially radially” or “substantially longitudinally”, it ismeant a radial or longitudinal extension with more or less 5°.

The plate 23 especially includes an upstream side face 30 and adownstream side face 31 extending generally radially, and a lower face32 extending longitudinally between the upstream side face 30 and thedownstream side face 31. The plate 25 further includes an upper face 25,extending longitudinally between the connection portion 24 and thedownstream side face 31. A nozzle guide upstream hook is intended torest upon said upper face 25.

The upper face 25 of the plate 23 adjoins a concave face 26 of theconnection portion 24, against which an end of the upstream hook isintended to bear.

The concave face 26 adjoins a radial face 27 of the base 22, havingitself formed thereon a rounded face 28 of the base 22, said roundedface 28 being directly connected to the casing body 21. It is noted thatthe concave face 26 and the radial face 27 are located on either side ofan edge 29.

Under the effect of the contact with the nozzle guide, the upper face 25of the plate and the concave face 26 are likely to be damaged. Yet, theconnection portion 24 being submitted to strong stresses, a machiningspringback is to be avoided on the concave face 26 of the connectionportion 24.

FIG. 3 schematically depicts the steps of a method 40 for repairing theupstream rail 20. The method 40 includes:

-   -   a step of covering 41 a surface with a solder 33, said surface        including the lower face 32, the downstream side face 31 and the        upper face 25 of the plate, and the concave face 26 of the        connection portion 24. Covering is performed so that the solder        33 extends substantially until the edge 29.

FIG. 4 shows the upstream rail 20 of the third turbine stage, at the endof the covering step. It is noted that, according to a preferredembodiment, covering is performed by Tungsten Inert Gas (TIG) welding,well known to those skilled in the art. Furthermore, the solder 33 isideally of the same material as the upstream rail, in order to avoidmaterial discontinuities in the repaired upstream rail.

-   -   A step of machining 42 the covered surface, from the lower face        32 of the plate 23 and in the direction of the radial face 27,        such that machining ends in the radial face 27. Indeed, a        machining springback in the radial face 27 is not likely to        embrittle the upstream rail 20, the area close to the vertical        line 27 being the least strained area of the upstream rail 20.        Machining is performed in a single action in order to avoid        intermediate machining springbacks, and possibly in several        passes. At the end of machining, the surface is reshaped,        suppressing wear traces on the upper face 25 of the plate 23 and        on the concave face 26 of the connection portion 24. FIG. 5        shows, with the thick line 34, the machining profile. It is        noted that the radial face 27 includes a machining springback        35.    -   A step of machining 43 the radial face 27 to suppress residues        of solder 33 which could have disseminated on the radial face        27. Machining is light, with a maximum depth of 0.1 millimetre.

This method enables an exit of the machining tool in the least strainedarea of the upstream rail (that is at the radial face) and remote fromthe wear area which initiated the repair.

It is noted that this method is adapted to repair upstream rails of allthe turbine stages, although these rails have slightly differentprofiles. Indeed, whatever the upstream rails to be repaired, they allhave a base including a radial face, a plate comprising an upper face,and a connection portion including a concave face.

1. A method for repairing an upstream rail of a turbine engine turbinecasing, said casing including a casing body extending along alongitudinal axis, said upstream rail including: a base including aradial face, extending substantially radially from the casing body, aplate including an upper face, extending substantially along thelongitudinal axis, a connection portion between the base and the plate,including a concave face connecting the radial face and the upper face,the concave face and the radial face extending on either side of anedge, said method including: covering a surface with a solder, saidsurface including the upper face and the concave face, such that saidsolder extends substantially until the edge, machining the coveredsurface, in a single action, in the direction of the radial face, and atleast until the edge, so as to reshape the surface.
 2. The repairingmethod according to claim 1, wherein machining the covered surface isperformed so as to end in the radial face.
 3. The repairing methodaccording to claim 1, further comprising machining the radial face. 4.The repairing method according to claim 1, wherein the covering isperformed by Tungsten Inert Gas welding.
 5. The method according toclaim 1, wherein the covered surface includes a downstream side face anda lower face of the plate.
 6. An upstream rail of a turbine engineturbine casing, repaired through a method according to claim 1.